As a ubiquitous and indispensable micronutrient in the human body, zinc ions (Zn2+) are present in every mammalian cell and play a pivotal role in a broad range of fundamental physiological functions. The forms of biological zinc can be divided into two categories: tightly bound zinc, which serves as structural and catalytic components of metalloprotein scaffolds, and mobile zinc, which exists in certain mammalian organs, including the brain, retina, pancreas, and prostate, and functions as an essential molecular signaling agent. The homeostasis of Zn2+, the process that controls a balanced level of the ion in all tissues, is strictly regulated under physiological conditions. When this process breaks down, as in diseases such as prostate cancer, there is a significant disruption of the proper, physiologically controlled levels of extra- and intracellular mobile [Zn2+]. The ability to measure and accurately quantify mobile zinc ions in these organs offers a potentially powerful method for early diagnosis of such zinc-related diseases, such as prostate cancer.
The healthy prostate contains high concentrations of mobile zinc, which decrease significantly during the development of prostate cancer, even at an early stage. Thus reduced zinc levels are a biochemical hallmark of prostate cancer development. The importance of diagnosing prostate cancer early is indisputable. Prostate cancer is the second leading cause of cancer death in men, exceeded only by lung cancer. According to the American Cancer Society, it accounts for about 13 percent of male cancer-related deaths. In its early stages, when it is still curable, prostate cancer causes no symptoms. Notably, the 5-year disease-specific survival rates for localized cancer are 100%. By contrast, metastatic prostate cancer is not curable and has an overall 5-year survival of just 33%. Life expectancy can be as low as 13 months, even in the presence of androgen-deprivation therapy. See Mannuel, H. D.; Hussain, A. Clin. Genitourin. Cancer 2006, 5, 43-9. Consequently, the ability to diagnose prostate cancer early, before it has spread beyond the confines of the organ, could offer the only possibility of a cure to patients at risk for aggressive disease. Indeed, with the advent of routine testing for serum prostate specific antigen (PSA), the 5-year cancer-specific survival rates have increased from approximately 70% in the early 1980s to over 90% just a decade later. The significance of early diagnosis and intervention is especially pronounced when considering younger men with a longer life expectancy. A recent study found that, in men under the age of 50, disease-specific survival at 16 years was 73%, whereas of the men treated with radical prostatectomy, 94% were alive at 21 years of observation.
There is thus an ongoing need for methods of treating and diagnosing prostate cancer and benign prostatic hyperplasia.